Made step to remove ASyncWindow in favour of usage of Future and FutureWatcher.

This should allow concurrency in the plugins to be independent from their container.

Contains also some work on the system for registering plugins.

pglab/plugin_support/ToolbarLocation.cpp

@@ -0,0 +1,14 @@
+#include "ToolbarLocation.h"
+
+ToolbarLocation::ToolbarLocation() = default;
+
+ToolbarLocation::ToolbarLocation(QString toolbar, QString group, int position)
+	: m_toolbar(std::move(toolbar))
+	, m_group(std::move(group))
+	, m_position(position)
+{}
+
+bool ToolbarLocation::isEmpty() const
+{
+	return m_toolbar.isEmpty();
+}